1. Field of Invention
This invention relates to heavy metalremoval from wastewater streams. More specifically the invention relates to the use of organic reactants to precipitate metals in solution.
2. The Prior Art
The use of organic reactants to precipitate metals in solution has been limited by poor regeneration of the reactants and the high costs of the reactants. Furthermore, large organic reactant consumption and poor settling and filtering properties are often encountered. In addition, the residual concentrations in the treated effluent often fail to meet applicable standards.
Organic reactants such as thioacetamide, dialkyl dithiocarbonates and starch xanthanes, have been proposed for the removal of soluble metals from waste effluents. [C. Brooks, Metal Recovery from Industrial Wastes, Journal of Metals, 38 (1986) 50.]
Husein et al. recently reported the use of compounds containing a sodium carboxylate group such as sodium caprate for the precipitation and removal of lead from aqueous solutions [M. Husein, J. Vera and M. Weber, Removal of Lead from Aqueous Solution with Sodium Caprate, Sep, Sci. Technol., 33 (1998) 1889.]
Meanwhile, organophosphorus reagents are known in solvent extraction. Solvent extraction is a separation technique wherein solubility characteristics are exploited to extract a given compound by dissolving it in a chosen solvent. Such reagents are considered suitable for the recovery and separation of cobalt and nickel from acidic leach solutions. [J. Preston, Solvent Extraction of Cobalt and Nickel by Organophosphorus Acids. I- Comparison of Phosphoric, Phosphonic and Phosphinic Acid Systems, Hydrometallurgy, 9 (1982) 115.] [P. Danesi, L. Reichley-Yinger, G. Mason, L. Kaplan, E. Horwitz and M. Diamond, Selectivity-Structure Trends in the Extraction of Co(II) and Ni(ll) by Dialkyl Phosphoric, Alkyl Phosphonic, and Dialkyl Phosphinic Acids, Solvent Extr. Ion Exch., 3 (1985) 435.]
However, the use of organophosphorus reagents and more specifically, sodium di-(n-octyl) phosphinate or sodium di-(n-dodecyl) phosphinate, have heretofore not been proposed for the recovery of lead, cadmium and zinc by precipitation. [W. Rickelton, Cobalt-Nickel Separation by Solvent Extraction with Bis(2,4,4-trimethyl pentyl phosphinic) acid, Solvent Extr. Ion Exch., 2 (1984) 815.] [A. Sastre, N. Meralles and E. Fignerola, Extraction of Divalent Metals with Bis(2,4,4-trimethyl pentyl) Phosphinic Acid, Solvent Extr. Ion Exch., 8 (1990) 597.] [M. Elizalde, J. Castresana, M. Aguilar and M. Cox, Extraction of Ni (II) from Nitrate Media by Di-n-Octylphosphinic Acid Dissolved in Toluene, Polyhedron 6 (1987)1251.]
Thus, it is an object of this invention to provide a novel, cost efficient organic reagent for precipitation of lead, cadmium and zinc from aqueous streams.